Method of fitting pistons to engine-cylinders.



W. McCORMACK & G. S. SEARLE.

METHOD OF FITTING PISTONS T0 ENGINE CYLINDERS. APPLICATION FILED MAR. 13, 1915.

1 181 467. Patel-m1 May 2, 1916.

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@QAMZJM WILLIAM MCCORMACK AND GEORGES. SEARLE, or ROCHESTER, NEW YORK.

METHOD OF FITTING PISTONS TO ENGINE-CYLINDERS.

Specification of Letters Patent.

Patented May 2, 1916.

Application filed March 13, 1915. Seria1 No. 14,154.

To all whom it may concern:

Be it known that we, \VILLLUL MCCOR- MACK and Gnoncn S. Snxnnn, both citizens of the United States, residing in Rochester, Monroe county, New York, have invented certain new and useful Improvements in Methods of Fitting Pistons to Engine-Cylinders; and we do hereby declare the following to be a full, clear, and exact description of the same, reference being bad to the accompanying drawings, forming a part of this specification, and to the reference-numerals marked thereon.

Our present invention relates to engines and more particularly to internal combustion engines and it has for its object to provide a simple, cheap and efficient method of fitting pistons to engine cylinders with such precision that less reliance need be placed upon the usual piston ring for holding compression and for preventing carbonization of the explosive chamber.

Features of the invention are also applicable to the refitting of worn cylinders and pistons and further objects of the invention are to enable cylinder and piston couples to be manufactured in the first instance with friction surfaces equal, if not superior to the surfaces produced through the use of the engine and further, to improve the quality of the material upon which the friction surfaces are formed.

To these and other ends the invention resides in certain improvements and combinations of parts all as will be hereinafter more fully described, the novel features being pointed out in the claims at the end of the specification.

In the drawings: Figure 1 is a top plan view partly in section of an apparatus for carrying out our invention. Fig. 2 is a section taken substantially on the line 66 of Fig. 1. Fig. is a transverse section taken substantially on the line 77 of Fig. 1, and Fig. 4 is an end elevation partly in section on the line 88 of Fig. 2.

Similar reference numerals throughout the several figures indicate the same parts.

It it well known in this art that the effects of wear on cylinders and pistons that have been in use for a long period of time are not wholly deleterious in that the quality of the wearing or friction surfaces is, in most instances, improved by becoming smoothed down to a high polish. The difiiculty is that by the time this has occurred the accuracy of fit between the cylinder and piston has decreased to such a degree that it is no longer effective to hold compression in the explosion chamber and to prevent the heavy lubricating oils from creeping up the walls of the cylinder around the piston and depositing carbon on the piston head, cylinder head and valves. The usual piston rings are, at their best, hiadequatc to prevent this last mentioned occurrence and besides, their effectiveness also becomes impaired.

By practising our invention, the piston that has become too small may be expanded or enlarged to again closely fit its cylinder with or without removing or changing the friction surfaces of either as circumstances may dictate.

The manufacture of piston and cylinder couples in the first instance as distinguished from the reforming or repair of worn couples should preferably be carried on 1n accordance with the invention described in our co-pending application, Serial No. 32,571, filed June 7, 1915, which is a division of this application. However the general manufacture is carried on, after the piston and cylinder have been smoothed down tofit each other approximately, they may be brought to an exact fit to give any degree of tightness desired and the quality of the wearing surfaces improved by a further treatment that our present invention provides and which consists in expanding the piston (l by peening the skirt thereof from the inside and by subjecting the interior surface to a multitude of light blows increasing the diameter uniformly to any degree desired within the limits that practice requires. This may be done by hand except that the confined space within which the hammer must be manipulated makes the process laborious and We therefore pre fer to use a suitable automatic peening machine such as that illustrated in the drawings and which will noW be described.

- In stationary bearings 10 on a base 11 is supporteda continuous shaft 12 carrying a chuck 13 that is connected at one end thereof by a suitable joint or coupling 14: made in two parts as shown which may slide transversely of the axis of the shaft because of dove-tail connections at right angles to each other. The piston 6 is placed in the chuck 13 by clamping the head of the piston between the jaws 15 by -means of a llO clamping ring 16 and when so mounted, the inner end or skirt of the piston rests upon the segmental anvil 17 formed 011 the base 11, the curvature of which anvil is approxi mate'ly that of the piston. The purpose of the connection 11 is to permit the piston to lie fiat and true upon the anvil at all times during the rotation thereof.

The anvil 17 is spanned by a transverse yoke frame 18 in which are journaled stationary centering rollers 19 at the sides that run in contact with the piston and hold it over the center of the anvil. Beneath a bridge piece 20 at the top of the yoke frame 18 is a vertically sliding block 21 operating in guides 22 and carrying a pair of rollers 23 which bear down upon the top of the piston and hold it in firm contact with the anvil 17 under the influence of a spring 24 housed within the block and bearing again st the bridge piece 20.

The shaft 12 is operated from a driving shaft 25 having a driving pulley 26 and journaled in fixed bearings 27 on the base 11. A ratchet wheel 28 is loosely mounted on the shaft 12 to turn relatively thereto but is adapted to turn the shaft through a chain of gearing embodying a gear wheel 29 fixed to the ratchet, back gearing 30 and 31 relatively fixed on a shaft 32 journaled in a bearing 33 on the base 11 and a gear 34: keyed to the shaft 12. Also loosely mounted on the shaft 12 is an arm 35 carrying a pawl 36 pivoted at 37 to cooperate with the ratchet wheel 28 and this arm 35 is vibrated by a link 38 pivoted thereto at 39 while the other end of the link is secured by a stud 40 in a slotted eccentric arm 41 on the driving shaft 25. Greater or less throw may be communicated to the arm 35 and its pawl 36 through the medium of the link 38 by changing the position of the eccentric stud 10 in the slotted arm 41 at a greater or less distance from the center of the shaft 25 according to a well known mechanical practice.

The inner end of the shaft 12 is threaded as shown at 42 and cooperates with a threaded nut 43 stationary on the base 11. Thus it will be seen that as the shaft 12 is rotated, it will simultaneously be given a longitudinal movement progressing continuously in one direction and the piston 6 will hence be rotated on the anvil 17 and also, by degrees, thrust longitudinally along the same. The lead of the screw 42 is very slight and it will be obvious from the nature of the driving mechanism described that the rate of rotation of the shaft 12 and hence of the piston 6 can be made exceedingly slow, so slow, in fact, as to be imperceptible and yet it may be regulated to a nicety within quite wide limits.

A rock shaft 14: journaled in bearings 45 on the base 11 carries a trip hammer embodying a radial arm eG-and a head 17 thereon offset to project within the yoke frame 18 so that it may vibrate within the interior of the piston (5 when resting on the anvil 17. The impact is given to the hammer bv av spring 18 encircling the shaft 11 and the hammer is raised against the tension of such spring by a cam 19 on the drive shaft 25 that cooperates with a trip arm on the hammer shaft 41. One blow of the hammer is thereforedelivered upon each rotation of the shaft 25 and hence upon each actuation of the chuck shaft 12, the arrangements being preferably such that the hammer blow is delivered while the link 38 is conducting the return movement of the pawl 36 and the work piece 6 is at rest.

With the relative movement of the hammer and the piston in these two directions, each blow is struck at a different point, though these points may be crowded as closely together asdesired and the whole interior surface of the skirt of the piston is gradually traversed. It may be gone over repeatedly if desired, but with a proper adj ustment of the machine, a single treatment is usually sufficient. This peening of the piston enlarges its diameter uniformly Without mutilating its outer frictional surface by spreading the metal. In fact, the effect upon, the material itself is distinctly advantageous, for its mass is condensed, closing the pores and permitting the frictional surface to assume a higher polish.

The peening operation alone is applicable to the refitting of worn pistons that have been in use in the engine a considerable length of time and it is here perhaps that it shows to the best advantage for the reason that the surfaces of both piston and cylinder are usually highly polished from having run in contact with each other so long and the only thing to be remedied is the lack of intimate contact between them. Our invention reestablishes that close fit without touching a tool to either part and preserves 'all the advantages that use has imparted in 'this one direction.

The usual previous method of repair was to discard the old piston and replace it With a new one of large diameter that fitted the cylinder closely but necessarily lacked the finish that the old one possessed.

In cases where either the piston or cylinder has been badly scored from some cause or other, requiring that its surface be turned down to remove the mutilation, our method may still be employed to save replacing a part, for the extent to which We can expand the piston is sufficient to compensate not only for the wear but for the removal of a thin chip from one or the other of the parts.

The excessive smoking of internal combustion engines, due to the creeping of the lubricating oil between the piston and the cylinder Walls can be entirely stopped by tightening the fit of the piston in accordance with our invention and the efliciency of the engine at the same time increased.

We claim as our invention:

1. The method of fitting pistons to engine cylinders which consists in enlarging the diameter of a relatively small piston by percussion.

2. The method of fitting pistons to engine cylinders which consists in enlarging the diameter of a relatively small piston by percussion, the blows being delivered at a plurality of points on a surface other than the friction surface of the piston.

3. The method of fitting pistons to engine cylinders which consists in enlarging the diameter of a relatively small piston by percussion, the blows being distributed over the inner surface of the skirt of the piston.

4. The method of fitting pistons to engine cylinders which consists in enlarging the diameter of a relatively small piston by the localized percussion of blows distributed over the inner surface of the skirt of the piston while the friction surface is being held against a support in contact therewith over an extended area.

WILLIAM MQCORMACK. GEORGE s. SEARLE.

Witnesses:

RUSSELL B. GRIFFITH, AGNES NESBITT BIssELL. 

